The hydroformylation of allyl alcohol is known and is utilized industrially (see e.g. U.S. Pat. Nos. 4,064,145; 4,215,077; 4,238,419; 4,678,857; 5,290,743). Allyl alcohol is reacted in these processes with CO/H2 gas mixtures, giving 4-hydroxy-butyraldehyde (HBA). Following distillative removal of undesired by-products, HBA is hydrogenated in a known manner to give 1,4-butanediol (BDO).
A disadvantage of this mode of production is the formation of undesired by-products. In particular, as well as the desired linear product, the isomeric branched product 3-hydroxy-2-methylpropionaldehyde (HMPA) and other C3 by-products such as n-propanol and propionaldehyde are formed. This adversely affects the economic viability of the process.
The present invention provides a process for producing 4-hydroxybutyraldehyde, characterized in that ally alcohol dissolved in polar solvents is reacted with CO and H2 in the presence of a catalytic system which is formed from a rhodium complex and a cyclobutane ligand which contains at least two trans-coordinated , 3,5 -dialkylphenyl-phosphinomethyl groups, with the exclusion of catalysts which contain an aliphatic, araliphatic or cycloaliphatic phosphine as ligand.